1. Field of the Invention
This invention is directed to magnetic bubble domain device systems, in general, and to an improved layout thereof, in particular.
2. Prior Art
Magnetic bubble domain device systems are known in the art. Various and sundry arrangements of such systems are also known. In addition, it is known to be used either one level systems or two level systems. In any such systems, magnetic bubble domain propagation paths are provided along with electrical signal conductors which are used for active (as opposed to passive) switching or other similar operations. In most of the known systems, the resistance produced by the conductor associated with the active devices is quite high and increases the power utilized by the system which contributes to thermal variations on the chip. In addition high resistance can require drivers with voltage levels higher than desirable in practical memory systems. The conductor resistance can be reduced by decreasing the conductor length or increasing its width as well as reducing or removing any bends corners and the like in the conductor. Moreover, it is highly desirable to eliminate conductor crossovers which are found in many two level active switches fabricated by non-planar processing techniques.
In general, in two-level type block switches and chip layouts, the conductor path for the active devices meanders across the chip surface. For example, the conductor paths meander back and forth between the minor loops and the major track or tracks in order to be applied to the switches therebetween. In order to reduce the disadvantageous effects of the two level type conductor, judicious design can be utilized. That is, the conductor can be arranged so as to include careful fabrication, careful sloping of conductor walls and/or by switching only alternate bits in the device pattern. However, these approaches cause the chips to be more expensive to fabricate.
In one-level switches, the conductor path is, typically, either permalloy or a multilayer composite one layer of which is permalloy (i.e. magnetic). This layer of magnetic material causes the design of single level switches to be somewhat difficult, especially in the regions outside of the propagation path. In this arrangement, a meandering type conductor in single-level devices has relatively high resistance because of long conductor paths and the large number of corners in the path. In co-pending application Ser. No. 628,293, now U.S. Pat. No. 4,079,359. Compact Transfer Replicate Switch for Magnetic Single Wall Domain Propagation Circuits, by I. Gergis, it has been suggested that the conductor path outside the active area can be removed or replaced by a non-magnetic conductor. This approach has the advantage of retaining a single high resolution mask while the magnetic film problems can be removed. However, an additional gross alignment step is required in the processing which renders the process relatively more expensive and time consuming.